Bug#266507: NPTL (0.60) quirks with pthread_create (ignores attributes)

[Florian Schmidt <mista.tapas@gmx.net>]

Package: libc6
Version: 2.3.2-ds1-16

Hi,

there's a problem with the libc6 package and a 2.6.x kernel. I have attached two test programs to illustrate the problem [test_thread_attr.cc and test_thread_post.cc; compile each with -lpthread].

The programs try to create a SCHED_FIFO thread. test_thread_attr tries this by setting the attributes before creating the thread. test_thread_post does this by using setschedparam explicitly after thread creation.

test_thread_attr fails silently. It reports no error ps -C test_thread_attr -cmL shows there are no SCHED_FIFO threads created:

mango:/home/tapas# ./test_thread_attr &
[1] 2235
mango:/home/tapas# ps -C test_thread_attr -cmL
  PID   LWP CLS PRI TTY          TIME CMD
 2235     - -     - pts/3    00:00:00 test_thread_att
    -  2235 TS   23 -        00:00:00 -
    -  2236 TS   23 -        00:00:00 -
    -  2237 TS   23 -        00:00:00 -

test_thread_post succeeds:

mango:/home/tapas# ./test_thread_post &
[1] 2250
mango:/home/tapas# ps -C test_thread_post -cmL
  PID   LWP CLS PRI TTY          TIME CMD
 2250     - -     - pts/3    00:00:00 test_thread_pos
    -  2250 TS   23 -        00:00:00 -
    -  2251 FF   50 -        00:00:00 -
    -  2252 TS   23 -        00:00:00 -

The failing of test_thread_attr is not expected behaviour and was afaik a crux introduced by the libc developers to work around some missing futex[?] stuff in the kernel. see:

http://www.redhat.com/archives/phil-list/2003-January/msg00122.html
http://www.redhat.com/archives/phil-list/2003-January/msg00123.html

http://www.redhat.com/archives/phil-list/2003-July/msg00047.html

But imho this (silently breaking posix conform applications) must not happen. Either an error should be issued by pthread_create, or it should succeed. The latter is the case with NPTL 0.61. 

http://www.redhat.com/archives/phil-list/2003-January/msg00122.html

basically has the one liner fix which could be applied to 0.60. Are there release plans for NPTL 0.61? 

thanks, 

florian schmit

-- 
Palimm Palimm!
http://affenbande.org/~tapas/

#include <pthread.h>
#include <unistd.h>
#include <iostream>

void *thread1_function(void*) {
	while(true) {
		// std::cout << "1" << std::endl;
		sched_yield();
		sleep(1);
	}
}

void *thread2_function(void*) {
	while (true) {
		// std::cout << "2" << std::endl;
		sched_yield();
		sleep(1);
	}
}


int main() {
	int error;

	// setup attributes for thread 1
	pthread_t *thread1 = new pthread_t;
	pthread_attr_t *thread1_attr = new pthread_attr_t;
	error = pthread_attr_init (thread1_attr);
	if (error != 0) 
		std::cout << "error in pthread_attr_init 1: " << strerror(error) << std::endl;
	
	error = pthread_attr_setinheritsched(thread1_attr, PTHREAD_EXPLICIT_SCHED);
	if (error != 0) 
		std::cout << "error in pthread_attr_setinheritsched 1: " << strerror(error) << std::endl;

	error = pthread_attr_setschedpolicy(thread1_attr, SCHED_FIFO);
	if (error != 0) 
		std::cout << "error in pthread_attr_setschedpolicy 1: " << strerror(error) << std::endl;
	
	struct sched_param *param = new struct sched_param;

	param->sched_priority = 10;
	error = pthread_attr_setschedparam(thread1_attr, param);
	if (error != 0) 
		std::cout << "error on setschedparam 1: " << strerror(error) << std::endl;
	



	// setup attributes for thread 2
	pthread_t *thread2 = new pthread_t;
	pthread_attr_t *thread2_attr = new pthread_attr_t;
	error = pthread_attr_init (thread2_attr);
	if (error != 0) 
		std::cout << "error in pthread_attr_init 2: " << strerror(error) << std::endl;
	

	// create the threads
	error = pthread_create(thread1, thread1_attr, thread1_function, 0);
 	if (error != 0) 
		std::cout << "error creating thread 1: " << strerror(error) << std::endl;

	error = pthread_create(thread2, thread2_attr, thread2_function, 0);
 	if (error != 0) 
		std::cout << "error creating thread 2: " << strerror(error) << std::endl;


	// hang around a bit
	while (true) sleep(1);

	return 1;
}

#include <pthread.h>
#include <unistd.h>
#include <iostream>

void *thread1_function(void*) {
	while(true) {
		// std::cout << "1" << std::endl;
		sched_yield();
		sleep(1);
	}
}

void *thread2_function(void*) {
	while (true) {
		// std::cout << "2" << std::endl;
		sched_yield();
		sleep(1);
	}
}


int main() {
	int error;

	// setup attributes for thread 1
	pthread_t *thread1 = new pthread_t;
	pthread_attr_t *thread1_attr = new pthread_attr_t;
	error = pthread_attr_init (thread1_attr);
	if (error != 0) 
		std::cout << "error in pthread_attr_init 1: " << strerror(error) << std::endl;
	

	// setup attributes for thread 2
	pthread_t *thread2 = new pthread_t;
	pthread_attr_t *thread2_attr = new pthread_attr_t;
	error = pthread_attr_init (thread2_attr);
	if (error != 0) 
		std::cout << "error in pthread_attr_init 2: " << strerror(error) << std::endl;
	

	// create the threads
	error = pthread_create(thread1, thread1_attr, thread1_function, 0);
 	if (error != 0) 
		std::cout << "error creating thread 1: " << strerror(error) << std::endl;

	error = pthread_create(thread2, thread2_attr, thread2_function, 0);
 	if (error != 0) 
		std::cout << "error creating thread 2: " << strerror(error) << std::endl;


	// do the SCHED_FIFO stuff _after_ thread creation:
	struct sched_param *param = new struct sched_param;
	param->sched_priority = 10;

	error = pthread_setschedparam(*thread1, SCHED_FIFO, param);
 	if (error != 0) 
		std::cout << "error set_schedparam 2: " << strerror(error) << std::endl;


	// hang around a bit
	while (true) sleep(1);

	return 1;
}